Make the peanut butter cup spread:
In a small bowl, combine the peanut butter, unsalted butter, confectioners' sugar, and vanilla extract. Mash with a fork and mix until combined. Set aside.
Make the s'mores dip:
Preheat the oven 450 degrees Fahrenheit.
To 4 3.5 inch mini cast iron skillets (you can use ramekins here), add the semi sweet chocolate chips, making sure to cover the surface of the skillet or ramekin completely. Dollop small amounts (I used a mini cookie scoop) of peanut butter cup spread over the chocolate chips. Arrange the marshmallow halves over the peanut butter cup spread and chocolate chips to cover the surface of the skillet. Place skillet in the oven for 6-7 minutes until the marshmallows have expanded, melted, and browned.
Remove from the oven, allow to cool for a minute, then have at it with some graham crackers.